Low-temperature digital computer component



July 5, 1960 V LOW-TEMPERATURE DIGITAL COMPUTER COMPONENT R. K. RICHARDS 2,944,211

Filed Jan. 2d, 1958 I4- u '2 I3 Fig. 2

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INVENTOR. Richard K. Richards 20 BY Fig. 6

2,944,211 Patented July 5, 1960 ice LOW-TEWERATURE DIGITAL COMPUTER COMIONENT Richard K. Richards, 0111 Troy Road, Wappingers Falls, N.Y.

Filed Jan. 20, 1958, Ser. No. 709,989

15 Claims. (Cl. 323-94) This invention relates to a low-temperature device, useful as a digital computer component, of the type known as a cryotron, which utilizes the superconductive phenomenon exhibited by some materials at low temperatures. More specifically, this invention relates to an improved cryotron structure.

A cryotron is a relatively new type of computer component and is described in some detail in a paper by D. A. Buck in the April, 1956-, issue of the Proceedings of the Institute of Radio Engineers, on pages 482493. Improved cryotron structures are described in my copending patent application Serial No. 661,143, filed May 23, 1957. The basic function of a cryotron device is to control the flow of current in one part of the device by means of the application of a signal to another part of the device. This function is achieved through the fact that a conductor in the extremely low-resistance or superconductive condition can be caused to change to the normalresistance condition by the application of a magnetic field to the conductor. Although the cryotron requires that the system be refrigerated to a very low temperature, there are many potential advantages in the use of cryotrons in digital computers, as compared with vacuum tubes, transistors, and other more conventional components. These potential advantages include very low power consumption, light weight, small size, low cost, and high speed.

The original cryotron geometry as described by Buck comprised a controlling wire wound in a helical pattern around a controlled wire. In the improved geometry described in aforementioned patent application Serial No. 661,143, the controlling wire is parallel to, and in some embodiments concentric with, the controlled wire. Both of the geometries just mentioned have the undesirable feature that a magnetic field is created external to the region encompassed by the elements of the structure. Such a magnetic field is undesirable because it causes unwanted interactions between adjacent cryotrons when closely spaced, and also because the large field-containing region creates an inductance which is larger than desirable for high speed operation. Also, in both geometries as described in the prior art, one or both of the controlling and controlled elements has its terminals at opposite ends of the device. Terminals at opposite ends are undesirable because at the high speeds contemplated it is desirable, in the interests of minimizing radiation from connecting Wires, to make interconnections among cryotrons by means of transmission lines comprised of closely spaced wires or comprised of coaxial conductors. To facilitate the connections to transmission lines it is desirable to have both connections to a given element at the same end of the device.

An object of this invention is to provide a cryotron structure for which the inductance of the controlling element is extremely small thereby permitting very high speed operation.

Another object is to provide a. cryotron structure with negligible external magnetic field thereby permitting close spacing of adjacent cryotrons in a machine.

Still another object is to provide a cryotron structure in which the terminals of each element are close together, or, more specifically, at the same end of the structure thereby facilitating the use of transmission lines for the interconnections among cryotrons.

A further object is to provide a cryotron structure for which the voltages induced in one element by magnetic coupling to the other element are minimized.

The basic principle of this invention involves a structure having a concentric arrangement of four conductors, two for the controlling element and two for the controlled element. The operation of the inner three of the four concentric conductors is substantially the same as in cryotrons of the prior art as described in my aforementioned patent application Serial No. 661,143. The novelty and objects of this invention are achieved by adding a fourth and outer concentric conductor to the device with certain appropriate connections between this conductor and certain other of the three conductors.

The various objects mentioned above, as well as other objects of the invention, are achieved as disclosed in the following description and the accompanying drawing, which disclose, by way of example, a preferred embodiment of the invention and the best mode which has been contemplated of applying the principles of the invention.

In the drawing:

Fig. l is a side view of a preferred embodiment of the invention;

Fig. 2 is an end view of Fig. 1;

Fig. 3 is a sectional view taken on the line 3--3 of Fig. 2; and

Figs. 4, 5 and 6 are side views of modifications of the preferred embodiment.

The preferred embodiment of the invention comprises four concentrically arranged circular cylindrical electrical conductors, 11, 12, 13, and 14, numbered consecutively from smaller to larger radii. These conductors are electrically insulated from each other, except for the connections to be described. The conductors are held in place by suitable means, not shown in the drawing, such as insulative bushings. In a preferred construction, the insulation and the conductors 12, 13 and 14 are built up on a central Wire, 11, through successive deposition or plating processes with the insulation acting as the supporting and positioning means for the conductors, in the manner shown and described in the above-mentioned copending patent application. Conductor 13 has a central lateral region 21, which is composed of a material different from the material of the remainder of theconductor 13 and the other conductors of the device, as will be described. In the embodiment of Figs. 1-3, the conductors l1 and 14 are connected electrically together by a wire 19 at one end of the device. At the opposite end, the conductors 11 and 14 are connected to terminals 17 and 18, respectively. Conductors 12 and 13 are com nected together by a wire 20 at one end of the device, this being shown in the drawing as the end corresponding to terminals 17 and 18. At the end opposite to the wire 2% the conductors 12 and 13 are connected to terminals 15 and 16, respectively. The connecting wires which are shown may, if desired, be replaced by conductivestraps or cup-shaped connectors, or the like. 1

All of the conductors and connections, except the region 21 of conductor 13, are preferably composed of a material which is a superconductor at the temperature of operation and in the presence of all magnetic fields normally encountered in the operation of the device, inorder to avoid resistive losses. With the device ,operating at a temperature of 4.2 K., niobium would be a suitable material. Ihe material of region 21 is chosen so that, at the temperature of operation, a magnetic field produced by a reasonably small current in conductor 11 or 12 will be capable of carrying the material into the normal-resistance condition although in the absence of a magnetic field this material will be a superconductor at that temperature. With a temperature of 42 K tantalum is a-suitablematerial for the region 21. It is possible, though not so desirable, for the region 21 to be expanded so as to constitute the entirety of the conductor 13. As shown, the end portions of the conductor 13 serve as conductive rings which insure a uniform crosssectional distribution of current in the region 21.

With the configuration as illustrated in Figs. 13, conductors 11 and 14 comprise the controlling element, and conductors 12 and 13 comprise the controlled element. It a current is passed from terminal 15 through conductor 12, wire 20, and conductor 13 to the terminal 16, the net magneticfield at the surface of conductor 13 including region 21, will be substantially zero because the field produced by the current in conductor 12 will cancel the field produced by the current in conductor 13. However, when a current is passed from terminal 17 through conductor 11, wire 19, and conductor 14 to terminal 18, the magnetic field at the surface of conductor 13 will not zlero. Instead, the field will be substantially equal to i that produced by current in the conductor 11 since current in a hollow circular conductor, 14 in this case, does not create a field within the conductor. Therefore, ourrentbetween terminals 17 and 18 is capable of influencing theresistance of the path between terminals 15 and 16, by causing the region 21 to be changed from the superconducting to the normal-resistance condition.

There is no magnetic fieldexternal to the device as portrayed the drawing,1e';goept for the relatively small amount caused by currents in the end terminals and co ne tions By chcc i t c dim n f the device so that the exposed parts at the ends, are sufficiently small, the magnetic effects of the end parts may be made as small as desired. The cancelling effects of fields from conductors 12 and 13 has already been mentioned. A s: ilar cancelling effect is obtained from the current in cgnductors 11 and 14, since vthe, current-flow is equal but in opposite directions in the two conductors.

Although the inductance of the straight conductor wire -11 is in itself quite small, the inductance of the entire controlling element comprised of conductors 11 and 14 iseven smaller. he reason for the small inductance can be understood bynoting that there are no flux lines surrounding conductor 14, andthe number of flux lines sprrounding conductor 11sis now limited to those lines Whlh can pass in the region between conductors 11 and 14., In the interest of very low inductance in the controlling element, it is desirable that the thickness of the conductors and various insulation layers be as small as possible; in other words, the radius of conductor 14 should be only slightly greater than the radius of conuc or 1- 1 The fact that the terminals 17 and 18 of the controlling element are at the same end of the device is apparent from thedrawing. Also, terminals 15and 16 of the controlled element are at the same end with respect to each other but not necessarily with respect to the terminals 17 and 18. The close proximity of .17 to 18 and of 15sto 16 allows coaxial wires or closely spaced transmission lines to be connected to the controlling andcontrolled elements with a minimum of stray magnetic fields, radiation, and other undesirable effects. 7

Although current in conductor 11 produces a magnetic field in conductor 13 as required for operation of the device, only a small net induced voltage occurs in the circuit between terminals 15 and 16 when the current in conductors 1 1 and 14, the controlling element, is changed. The reason is that the voltage induced in conductor 13 is 7 approximately cancelled by a similar induced Voltage in 2,944,211 A H H A V l 4 conductor 12, but of opposite polarity with respect to terminals 15 and 16. Similarly, only small voltages are induced in the controlling element by a changing current in the controlled element. The reason in this case is that current flow between terminals 15 and '16 is in opposite directions in conductors 12 and 13 so that the net flux linkage with either 11 or 14 is substantially zero.

A variation in the preferred embodiment of this invention can be obtained by connecting all four of the terminals 15, 16, 17, and 18 to their respective conductors at the same end of the device, with wires 19 and 20 being connected at the opposite end, as shown in Fig. 4. Also, the roles of conductors 11 and 12 can be interchanged by making appropriate connections as shown in Figs. 5 and 6. With this variation, the magnetic coupling between the controlling and controlled elements is less easily visualized. Further, additional pairs of concentric conductors can be added to increase the number of con trolling or controlled elements, or both. Either the controlling-or controlled elements of other cryotrons can be insertedin series with the connecting wires 19 and 20.

It has been shown, by way of example, how elements made of materials exhibiting superconducting properties can be assembled to provide a new device for the control of the flow of current in one part of the device through the action of a current in another part of the device wherein certain desirable properties are obtained such as no magnetic fields external to the device and such as an extremely small inductance of the controlling element. It is to be understood that the above-described preferred embodiment, and variations thereof, are illustrative of the applications of the principles. of this invention, and

of the conductors lying therewithin thereby providinga' controllable'element, and means electrically connecting anotherone of the conductors lying within said first con ductorsto one of the conductors lying without said first conductor thereby providing a control element, whereby the conductivity of said controllable element can be controlledby a magnetic field produced by current flowing in'said control element.

2.7 A cryotron device comprising at least four concentrically arranged elongated electrical conductors, at least a first one of said conductors other than the two inner.- most' conductors comprising a material having superconductive characteristics which can be, afiected'by a magnetic field, means electrically connecting said first conductor in series with one of said innermost conductors thereby providing a controllable element, and means. electrically connecting'the other one of said innermost conduct ors in-series withone of the conductors lying with out said first conductor thereby providing a control element, whereby the conductivity of said 'controllablelelement can be controlled by a-magnetic field produced by current flowing in said control element.

s '3. A cryotron device as claimed in claim 2,' in which each-of saidmeans for connecting conductors'in series comprises. an electrical connection between an end of one of the series-connected conductors and the correspondingend-of the otherof the series-connected conductors.

, 4. A cryotron device comprisingat'least four concentrically arranged elongated electrical conductors, at least a first one of said conductors other than the tWo-innen rnost conductors comprisinga m aterial h aving superconductive characteristics which can be affected by a magnetic field, means electrically connecting said first conductor in series with one of said innermost conductors thereby providing a controllable element, and control means connected to pass current in opposite directions through the other one of said innermost conductors and one of the conductors lying without said first conductor thereby to produce a magnetic field for controlling the conductivity of said controllable element.

5. A cryotron device as claimed in claim 4, in which said first conductor has a region intermediate the ends thereof which is made from said material having superconductive characteristics.

6. A cryotron device as claimed in claim 4, in which all of said conductors comprise material having superconductive characteristics which can be affected by a magnetic field, the material of all of the conductors other than said first conductor having the characteristic of remaining superconductive during normal operation of said device.

7. A cryotron device comprising a first elongated electrical conductor, second, third and fourth elongated electrical conductors of hollow cylindrical shape arranged concentrically in the named-order about said first conductor, the third one of said conductors comprising a material having superconductive characteristics which can be afiected by a magnetic field, first connecting means electrically connecting an end of said third conductor to the corresponding end of one of said first and second conductors to form a first series circuit, second connecting means electrically connecting an end of said fourth conductor to the corresponding end of the other one of said first and second conductors to form a second series circuit, and terminal means respectively connected to the remaining ends of said conductors, whereby the conductivity of said first series circuit can be controlled by a magnetic field produced by current flowing in said second series circuit.

8. A cryotron device as claimed inclaim 7, in which said first and second connecting means are at opposite ends of said device.

9. A cryotron device as claimed in claim 7, in which said first and second connecting means are at the same end of said device.

10. A cryotron device comprising a first elongated electrical conductor, second, third and fourth elongated electrical conductors of hollow cylindrical shape arranged concentrically in the named order about said first conductor, the third one of said conductors comprising a material having superconductive characteristics which can be affected by a magnetic field, first connecting means electrically connecting an end of said third conductor to the corresponding end of said second conductor to form a first series circuit, second connecting means electrically connecting an end of said fourth conductor to the corresponding end of said first conductor to form a second series circuit, and terminal means respectively connected to the remaining ends of said conductors, whereby the conductivity of said first series circuit can be controlled by a magnetic field produced by current flowing in said second series circuit.

11. A cryotron device as claimed in claim 10, in which said first and second connecting means are at opposite ends of said device.

12. A cryotron device as claimed in claim 10, in which said first and second connecting means are at the same end of said device.

13 A cryotron device comprising a first elongated electrical conductor, second, third and fourth elongated electrical conductors of hollow cylindrical shape arranged concentrically in the named order about said first conductor, the third one of said conductors comprising a material having superconductive characteristics which can be affected by a magnetic field, first connecting means electrically connecting an end of said third conductor to the corresponding end of said first conductor to form a first series circuit, second connecting means electrically connecting an end of said fourth conductor to the corresponding end of said second conductor to form a second series circuit, and terminal means respectively connected to the remaining ends of said conductors, whereby the conductivity of said first series circuit can be controlled by a magnetic field produced by current flowing in said second series circuit.

14. A crotron device as claimed in claim 13, in which said first and second connecting means are at opposite ends of said device.

15. A cryotron device as claimed in claim 13, in which said first and second connecting means are at the same end of said device.

References Cited in the file of this patent UNITED STATES PATENTS 2,666,884 Ericsson et a1. Jan. 19, 1954 

